Crown Preparation — ORE Part 1 MCQ
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Correct answer: E — 1.5-2.0 mm
Explanation lettering: D = shown as A · E = shown as B · B = shown as C · C = shown as D · A = shown as E
The correct answer is A (1.5–2.0 mm). Established prosthodontic standards require approximately 2 mm of occlusal clearance for porcelain crowns on anterior teeth. This range accommodates the thickness needed for both the metal coping and the porcelain veneer while ensuring adequate porcelain bulk for strength and esthetics. For functional anterior teeth (canines), the lower end (1.5 mm) is acceptable in conservation-minded preparation, but 2 mm is the classical standard. Options B (0.5 mm) and E (0.3 mm) are insufficient to accommodate porcelain thickness; option C (1.0 mm) may be marginal for adequate porcelain bulk; option D (3.0 mm) represents unnecessary and excessive tooth reduction.
Reference: Prosthodontic preparation guidelines establish 1.5–2.0 mm occlusal clearance for porcelain crowns. See: USPTO Patent 4708649 'Occlusal clearance indicator' (1988) and clinical trial standard protocols for PFM crown fabrication.